The White House has confirmed that Ukraine is using US cluster bombs against Russian forces in the country.
National Security Spokesman John Kirby said initial feedback suggested they were being used "effectively" on Russian defensive positions and operations.
Cluster bombs scatter multiple bomblets and are banned by more than 100 states due to their threat to civilians.
The US agreed to supply them to boost Ukrainian ammunition supplies.
Ukraine has promised the bombs will only be used to dislodge concentrations of Russian enemy soldiers.
"They are using them appropriately," Mr Kirby said. "They're using them effectively and they are actually having an impact on Russia's defensive formations and Russia's defensive manoeuvring. I think I can leave it at that."
The US decided to send cluster bombs after Ukraine warned that it was running out of ammunition during its summer counter-offensive, which has been slower and more costly than many had hoped.
President Joe Biden called the decision "very difficult", while its allies the UK, Canada, New Zealand and Spain opposed their use.
The vast majority sent are artillery shells with a lower than 2.35% "dud rate", a reference to the percentage of bomblets which do not explode immediately and can remain a threat for years.
The weapons are effective when used against troops in trenches and fortified positions, as they render large areas too dangerous to move around in until cleared.
Russia has used similar cluster bombs in Ukraine since it launched its full-scale invasion last year, including in civilian areas.
Reacting to the US decision to send the bombs, Russian President Vladimir Putin said his country had similar weapons and they would be used "if they are used against us".
Oleksandr Syrskyi, the Ukrainian general in charge of operations in the country's east, told the BBC last week that his forces needed the weapons to "inflict maximum damage on enemy infantry".
"We'd like to get very fast results, but in reality it's practically impossible. The more infantry who die here, the more their relatives back in Russia will ask their government 'why?'"
He added however that cluster bombs would not "solve all our problems".
He also acknowledged that their use was controversial, but added: "If the Russians didn't use them, perhaps conscience would not allow us to do it too."
Yeah, but the big difference is these are small bombs, and a ton of them, that are really difficult to detect and clear. These things can be a buried for decades, and unlike a mine field someone could have walked or driven over it a thousand times before the one time it finally goes off or gets unearthed and someone picks it up not knowing it's about to kill or maim them. And the place they're dropping them might not be an urban area now, but what about in 40 years? The ones the US dropped on Laos, for example, are still killing people. There are millions and millions of them still to this day.
I disagree. Russia has already deployed millions of minds inside of Ukraine, which is a foreign country. Those mines will stay active and deployed for decades, if not hundreds of years just waiting for something to drive or step on them before they explode.
Don't forget the so-called butterfly cluster bombs which have been used by Russia which changes color to a bright orange that makes it look like a toy to kids.
UXOs are in a state because the fusing failed. However, many of the clustered munitions that the United States still has in its inventory have a dual fuse to mitigate and reduce the number of UXOs to a very small percentage of the submunitions.
Germany years ago even developed cluster munitions with an electronic fuse that would completely fail within 24 hours of being deployed. Those had a 0% UXO rate. It's too bad that the United States military hadn't adopted that fusing system instead but it probably had other drawbacks.
In addition to the mines so, there are thousands of unexploded artillery shells that have been fired from both sides that are also a hazard.
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My point is that it is way too late in the game to be complaining about certain types of munitions being used when any sane line in the sand has long been crossed by the egregious war crimes being committed on a daily basis by Russia. Well the human rights watch can complain about Ukrainian war crimes, this whole shit storm was kicked off by Russia and they still defend their genocidal campaign against Ukrainians.